1. Field of the Invention
This invention relates to methods for controlling growth of harmful organisms in water, particularly algae blooms generated by red tide organisms.
2. Introduction to the Invention
Red tide blooms occur in marine waters throughout the world and can be detrimental to the environment, human health, and marine life, and can result in severe economic impacts to tourist industries. The economic effects of red tide blooms can be particularly detrimental in ocean-bordering states such as Florida that rely heavily on revenue generated through tourism.
The causative organism of the Florida red tide is the dinoflagellate Karenia brevis (Davis), formerly known as Gymnodinium breve and Ptychodiscus brevis. Although found primarily in the Gulf of Mexico, K. brevis has been transported by ocean currents as far as the Atlantic seacoast. K. brevis blooms have been reported since the mid-1800's and have been accompanied by massive fish kills, poisonous clams, and associated respiratory irritation.
Red tide blooms are also known as harmful algal blooms (HAB) and produce toxic compounds known as phycotoxins, red tide toxins, or HAB toxins. K. brevis produces a suite of polyether neurotoxins called brevetoxins. Toxins produced by HAB affect public health by accumulation in seafood, by inhalation, and by skin contact. The Florida red tide organism has been implicated in extensive fish kills in the Gulf of Mexico, as well as in other animal mortalities. Red tide toxins were reported as the cause of death in over 150 endangered Florida manatees in 1996 and over 100 dolphins during 1999–2000 and again in 2004. The adverse effects of red tides on public health, marine life, the environment, and natural resources, are extensive.
Certain algal species are prevalent in different regions of the world and additional harmful species are being identified at a rapid pace, with as many as 100 species of toxic microalgae identified in the marine environment. The global increase in frequency and intensity of harmful algal blooms has led to more frequent incidence of seafood-borne illnesses and greater impacts on natural resources. The recent increase in number and intensity of HABs has raised concern that toxic phytoplankton species may be replacing nontoxic species. With increasing numbers of toxic species impacting aquatic organisms as well as public health, new and innovative techniques are necessary to control growth and mitigate the effects of these organisms. Considerable effort is being directed towards development and refinement of innovative techniques to meet increasing demands for protection of public health, aquaculture, and natural resources.
Ozone is a commonly used and powerful oxidizing agent for cleaning and purifying water. It is used extensively as a sanitizer in swimming pools, and for purification of drinking water and aquarium water housing fish, marine mammals, and other marine life. Ozone has been shown to be effective in inactivating crude toxins associated with dinoflagellate blooms, as well as in reducing the levels accumulated in shellfish (Blogoslawski, W. J., F. P. Thurberg, M. A. Dawson, and M. J. Beckage, 1975, “Field studies on ozone inactivation of a Gymnodinium breve toxin,” Environmental Letters, 9(2):209–215, Blogoslawski, W. J., F. P. Thurberg, and M. A. Dawson, 1973, “Ozone inactivation of a Gymnodinium breve toxin,” Water Research, 7:1701–1703). Ozone has been used to treat seawater in marine laboratories dependent upon a non-toxic source of natural seawater.
Typical methods for controlling growth of red tide organism using ozone, such as those currently employed by aquaria, effectively destroy red tide organisms and associated toxins. Existing methods, however, involve the use of very high ozone concentrations and are accompanied by many drawbacks, including high expense, human health hazards, and detrimental effects on aquatic species. In aquaria, over-ozonation of water sources is usually necessary in order to destroy high levels of toxins. These high levels of ozonation, and the by-products of oxidation, e.g., salts, are generally harmful to other marine species.
Others have described the use of ozone to kill red tide organism. For example, U.S. Pat. No. 6,235,206, the disclosure of which is incorporated herein by reference, discloses a method wherein ozone is injected directly into water containing red tide algae. However, the direct injection of ozone into a marine environment does not directly target the red tide blooms and the resulting uncontrolled or high levels of ozone and its by-products can be harmful to the environment and marine species. Therefore, the method requires monitoring of both ozone concentration and dissolved oxygen content in the water to prevent harm to marine life in the water. Also, the treated (i.e., ozonated) water can interchange continuously with harmful organism-containing water, leading to an inefficient and uncontrolled process. In addition, the method requires the transportation of elaborate equipment to the treatment site. U.S. Pat. No. 6,451,612, the disclosure of which is incorporated herein by reference, discloses a method for determining a level of ozone that should be used to treat water by measuring an initial content of oxidants in the water to be treated, and then taking a sample of the water to be treated and systematically inducing a calibrated solution of known ozone concentration therein and measuring the resulting oxidant concentration after a specified time. The appropriate concentration of ozone for treating the water is then arrived at using the oxidant concentration of the water sample after injecting with the calibrated solution. However, this method is time and labor intensive, and only addresses the determination of a level for ozonation, and does not provide a delivery method for that level.
Therefore, there exists a need for an efficient, effective and safe method for using ozone to control growth of red tide organisms while not harming other marine species.